A scanner, aside from the keyboard and mouse, is a widely used computer input device. It can be used to input photos to generate personal electronic picture files, or input pictures to set up a personal Web site. Or hand-written letters may be sent by scanning and E-mail to replace FAX machines. The scanner can also be coupled with OCR software to enter contents of newspapers or books without the tedious labor of manual data entry. All this shows the powerful functions of the scanner. It greatly improves the efficiency in offices, learning and recreation.
The scanner achieves its functions mainly by digitizing the picture. Light is emitted from a lamp and reflected to a document held on a glass plate of the scanner. The bright and dark differences of the document form reflection light of different intensity. The reflection light passes through a series of reflection mirrors and focuses on a CCD at another end of the lens. The CCD transforms optical signals to correspond electric signals, namely analog signals. These signals are transformed by an A/D converter to become digital signals recognizable by computers. Through various interfaces such as an EPP (Enhanced Parallel Port), USB (Universal Serial Bus), or SCSI (Small Computer System Interface), the digital signals are sent to a computer.
The A/D converter is a semiconductor element for transforming the analog signals to digital signals. The electric signals obtained by the CCD are simulated signals corresponding to the brightness and darkness of the image. Namely, variations from the darkness to brightness of the image can be indicated by different electric potentials. They are changed continuously, and are called simulated amount.
In the scanner, the light source is important. The light sensed by the CCD is emitted from the lamp of the scanner. Impure or polarized light directly affects the scanning result. The professional scanners or some high-end home or office scanners automatically test the light intensity emitted from the lamp before scanning, especially when the scanner has just been powered on. As the lamp is not yet stable, and the scanner has a specific warm up period, only when the light intensity reaches the required standard will the light testing sensor in the scanner issue an approval instruction. Then the scanner can reach the optimal condition to process scan operation. Otherwise the light intensity cannot effectively present the details of the dark portions of the document.
Conventional scanners generally use a cold cathode fluorescent lamp (CCFL) as the light source. Such a lamp has a big drawback, it requires a warm up time when the scanner is powered on each time to enable the brightness of the lamp to increase to a stable condition. The warm up time could last about 1-3 minutes. This is according to many users not acceptable. Some users even mistakenly deem it as machine malfunction and request product return. This is especially significant and serious in a low temperature environment.
In view of the foregoing problems, some vendors have tried to use a light emitting diode (LED) as the light source of the scanner. While the LED can reduce waiting time when the scanner is cold started, it has some drawbacks such as a not adequate brightness and serious heat dissipation problem.